It really depends on the situation but in general Plasma is the way to go. Below is my assessment of the 4 technologies.
-Plasma pros:
Offers the brightest picture with highest possible contrast.
Each pixel illuminates itself rather than depending on a back light or projector bulb.
Blacks are black, not blue or gray since black is created by the pixel NOT emanating light, rather than blocking light.
nearly 180° degree left/right/up/down viewing angle
- Plasma Cons
It is possible to "burn in" an image to the screen if you leave a high contrast image static on the screen for a long period of time. (Not likely on new sets unless VERY negligent, but it is possible)
Reflective surface on screen could cause glare.
Set is heavy in comparison to LCD and must be transported upright (you shouldn't lay a plasma screen horizontally when moving it)
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LCD Flat Panel Pros
Light, easy to move and transport any way you want (really you shouldn't lay them down, but its not as critical)
Generally less expensive than plasma.
Absolutely no possibility of burn-in of an image on the screen
No reflective surface on screen so no glare in bright rooms or with poorly placed lamps.
-LCD Flat Panel Cons
Limited viewing angle on some models, even the ones with wide viewing angles (especially vertically), there is a "sweet spot" so the picture is not consistent everywhere in the room.
No "true black" LCD sets make black by blocking the back light shining though the LCD membrane. Though some more expensive models are great, no LCD flat panel blocks 100%. So LCD flat panel black is a very dark gray or blue. Not black.
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DLP Pros
- Large screen for the money.
- Very bright picture.
DLP Cons
Some models have very expensive bulbs that need to be replaced periodically. Some DLPs now have an LED bulb which make it more attractive.
Limited viewing angles
Screen will yellow over time. (YES IT WILL!
)
Requires periodic cleaning INSIDE unit to keep it looking "like new" (YES, it does)
No "true" black, though very good.
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Projector Pros
-Can have a HUGE picture projected on a whole wall.
-Versatile, easy to move from one place to another and have a true "theater"
-Versatile again...you can chose picture size depending on situation at a whim with most models!
Projector Cons
Picture quality dependent on what is used as a screen. A white wall vs a real screen surface or even a white bed sheet can drastically affect how good the picture looks. All would look good, but to compete on a PQ basis with the other three, you really need a true "screen" and smaller size concentrating more light on the smaller area making a very bright clear image. A 100" image would not look anywhere near as bright or clear. It will look great, but not "as great".
Bulbs can be very expensive and need to be replaced periodically.
Projectors have LCDs in them too, so they are also subject to the "true black" limitations.
You must have a dark room or at least projection area to get the best results from a projector. Hard to do in a living room with large windows during the day unless you want to live in a cave atmosphere or have the money for a "home theater room".
When people walk in front of the projector, they block the image...silly to say but essentially some one can block everyone's view when they get up for another bowl of cheetos!
wanted another FPTV but, not logical for the use it will get... leery of Plasma's...
flipped a coin twice and it lost the battle between it and a Samsung, went with it anyway... 
